Island Diversification research by curator Rafe Brown and a large group of students and colleagues in the U.S. and the Philippines focuses on land vertebrate biogeography across a dynamic and complex island archipelago.

Island life has fascinated biologists for centuries. In addition to many bizarre and enigmatic species like giant flightless birds, miniaturized pygmy mammoths, and colossal tortoises and monitor lizards, island forms of plants and animals have inspired philosophers and evolutionary biologists to conceive of many of history’s most contemplative theories and insightful paradigm shifts. It is no wonder that islands played a central role in Alfred Russell Wallace’s and Charles Darwin’s conception of the fundamental mechanisms of evolution by natural selection and that the archipelagos of the western Pacific served as the backdrop for the formulation of several highly influential macroevolutionary hypotheses: equilibrium theory biogeography, the taxon cycle, the great speciator, supertramps, assembly rules, the biological species concept, etc.

The Philippine archipelago is an ideal geographical system for testing predictions regarding the production, partitioning, and maintenance of biodiversity in a dynamic archipelago setting with a well-studied geological history. Given our detailed knowledge of variable patterns of land connectivity, sea level fluctuations, landmass subduction, and accretion, and paleo-transport along the Philippine “Mobile Belt,” researchers can readily formulate predictive models and test classic evolutionary hypotheses from earlier works, with genetic/genomic data, population genetic methods, phylogenies, and information about species distributions.

Built on a foundation of earlier undergraduate and graduate work, Brown’s long-term interests in biodiversity and conservation of Philippine vertebrates has become focused on testing biogeographical hypotheses with phylogenies, species distribution information, population genetic approaches, most recently with genomic data and robust geographical and multi-taxon comparative frameworks. With data from numerous co-distributed Philippine radiations of amphibians, reptiles, birds, and mammals now available, we can test general synthetic predictions relevant to all faunal groups: are species distributions predominately governed by ecological or historical factors? Did vertebrate diversification accelerate immediately following the emergence of the major volcanic components of the archipelago? Did the species-pump mechanism of Pleistocene sea-level oscillations contribute substantially to diversity accumulation? How have ancient landmass movements and connectivity facilitated or limited colonization and subsequent diversification? What role do elevational, ecological and atmospheric gradients played in accumulation of land biodiversity? Have the sensationally diverse and endemic Philippine clades been produced by adaptive, non-adaptive, or a combination of processes?

The approaches have been numerous and continue to develop, but common themes in our works include well-sampled empirical studies, phylogeny estimation, statistical approaches to hypothesis testing, and collaborations with many students and museum-based researchers on both sides of the Pacific.

Esselstyn JA, Maher SP, BrownRM. 2011. Species interactions during diversification and community assembly in an island radiation of shrews. PLoS One 6:e21885

Esselstyn JA, Brown RM. 2009. The role of repeated sea-level fluctuations in the generation of shrew (Soricidae: Crocidura) diversity in the Philippine Archipelago. Molecular Phylogenetics and Evolution 58:171–81.

Esselstyn JA, Oliveros CH. 2010. Colonization of the Philippines from Taiwan: a multi-locus test of the biogeographic and phylogenetic relationships of isolated populations of shrews. Journal of Biogeography 37:1504–14.